I have a puzzle that I need some help with

 

Last year I replaced the wheelbearing and the ABS sensor on the left front side  (Drivers side in Denmark). And it worked fine until 2 months ago. I braked a bit hard, and the ABS sensor light came on. I have tested the car, and the faultreader says improbable signal from the ABS sensor on the front left hand side. 

 

With my multimeter I have tested that the wiring all the way from the ABS sensor to the ABS block is intact. So those wires are good. 

 

I have tried to spin the wheel with a multimeter connected to the sensor, to see if I could get a reading. But I could not get it to work. Maybe my multimeter was not sensitive enough. 

 

What is strange is that when I drive the car on the road, the ABS warning light comes on immediately. But when the car is resting on axle stands, and I put it in 1. gear or 2. gear and simulates driving, and I use the brakes, the warning ligths does not come on!!!!!

 

What could be the cause of that?? . Faulty wheelbearing although it is not even 1 year old?. A faulty ABS sensor? Any suggestions?

 

Regards, Søren

 

Copenhagen, DK

Skoda Fabia Combi 2004, 1.2 L petrol. 

 

 

Take the driveshaft out of the hub and check to see the sensor is sat close to the bearing. 

Hello Techle. 

Thanks. I will check that. That could make sense,

Regards, Søren

"Improbable signal" is VAG-speak for actual value < lower_bound OR actual value > upper_bound

Hello Ken

And what does that mean in plain english? That the signal is not strong enough? 

 

Cheers, Søren 

Implausible Signal.

Hello TMB. Yes you are right. I found out that the faultcode 16885 is "implausible signal". But still I am not quite sure what that means,

It means it it is seeing something but the signal is not what it is expected. 

Ahh. So it couldbe a faulty abs sensor. I bought a fairly cheap one, that maybe does not have the right resistance. Or maybe the wheelbearing. I Will have to look more into that. Thank you Techle. 

I had the same problem on changing a front wheel bearing on our Roomster. ABS light up for months afterwards, when I changed warped disc I disconnected ABS sensor switch. It cleared fault on reconnection, probably dirty or bad connection.

I took the steering knuckle off and showed it to a certified mecahinc. He said that the bearing is fully seated, but gap between the sensor and magnetic ring was to wide. So I got home and brought the gap  down to 1 mm. But still no success. Does anyone know what the correct distance should be - am I whithin spec.?

 

Also when I measure the 4 abs sensors resistances they all read within the area 13 MOhm. Everywhere i look it states that the sensor should be within the range from 1 KOhm - 1.6 KOhm. And my Ohms are way bigger that that. But wouldn´t there be a fault on all 4 sensors then, and not only on the front left wheel? They are all from the same brand  ATEC. And my multimeter is a Bryman 257, so it is not the cheapest crap out there.

 

Can anyone explain to me what the devil is going on?????

 

Cheers, Søren

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

On 26/06/2019 at 22:19, Tech1e said:

Take the driveshaft out of the hub and check to see the sensor is sat close to the bearing. 

 

There is a 1 mm gap between the sensor and the bearing - is that to close?

1 hour ago, soerenfink said:

I took the steering knuckle off and showed it to a certified mecahinc. He said that the bearing is fully seated, but gap between the sensor and magnetic ring was to wide. So I got home and brought the gap  down to 1 mm. But still no success. Does anyone know what the correct distance should be - am I whithin spec.?

 

Also when I measure the 4 abs sensors resistances they all read within the area 13 MOhm. Everywhere i look it states that the sensor should be within the range from 1 KOhm - 1.6 KOhm. And my Ohms are way bigger that that. But wouldn´t there be a fault on all 4 sensors then, and not only on the front left wheel? They are all from the same brand  ATEC. And my multimeter is a Bryman 257, so it is not the cheapest crap out there.

 

Can anyone explain to me what the devil is going on?????

 

Cheers, Søren

How did you bring the gap down?

How was the new bearing fitted? With correct tooling?

 

I think the resistance measurements you've seen suggested may be for a different type of sensor (VR).

14 minutes ago, Wino said:

How did you bring the gap down?

How was the new bearing fitted? With correct tooling?

 

I think the resistance measurements you've seen suggested may be for a different type of sensor (VR).

 

Hello Wino

 

Thank you for responding.

 

I filed the surface where the bolt goes in flat. Because of rust the surface was not flat, which resulted in the sensor being dragged away from the sensorring, when I tightened the bolt down. When filed flat it brought the gap down. Plus I removed some rust from the sensor hole with a dremel. 

 

I put the bearing in with a handheld bearing tool, that should be designed for it. There is a link here  www.ebay.co.uk/itm/264303991856

 

I will buy a new sensor tomorrow from a different brand and try that out. And if that not works I will remove the driveshaft and check the bearing magnets with a "card" that I bought. 

 

Any other ideas/thoughts?

 

Cheers, Søren

 

 

 

 

3 minutes ago, soerenfink said:

new sensor tomorrow from a different brand and try that out

Good plan, I think.

Today I did another experiment with the ABS sensor. 

 

I suspected that the wiring going to the sensors might be bad, and wanted to test if the fault was on the "sensor/hub" side, or on the "harness side". So I connected the wiring going to the left front wheel, with the sensor on the right hand side (with a fairly long wire). And then I connected the wiring going to the right front wheel sensor, with the sensor on the left wheel (also with a fairly long wire).  And then I erased all the faults with my little chinese scan tool. Originally my fault is a 16885 - implausible signal on the left front wheel. 

 

If I would get a fault on the right hand side on my scan tool, then my "sensor/hub" would be bad - since the left hand sensor now would be connected to right hand side wire

 

If I would get a fault on the left hand side on my scan tool  (As it has been so far), then my "wiring harness side" would be bad - since the left hand wiring would be connected to the sensor on the right hand side (previously no fault).

 

I took it for a small drive, and the same error came up 16885 - implausible signal on the left hand side. So I guess it is the wiring  going to the sensor on the left hand side that is bad, if my reasoning is right. It´s not shorted or open ( I have tested that), but I suspect that it is partially broken or corroded somewhere in the wiring. That would also fit with the experience that when the car  is on axle stands, and I put it in gear and drive it, I dont get a warning signal on the ABS. Probably because nothing is moving the wires, and "provoking" a bad connection, when the wheels are hanging freely in the suspension. 

 

Any thoughts on my reasoning?

 

Cheers, Søren

Very nice experiment. 

Replace wiring between ABS module and left front sensor next, I guess?

5 minutes ago, Wino said:

Very nice experiment. 

Replace wiring between ABS module and left front sensor next, I guess?

 

Yes, I think so. But it does look a bit complicated, because I can´t really follow the wiring going from the wheelarch to the engine bay. It somehow dissapears into the chassis, and then comes out again in the engine bay. But maybe I will do a shortcut and just replace the part of the wire that is in the wheelarch, since I suspect that´s where my corroded /faulty wire is. It seems like a lot of hassle to replace the whole wire. 

 

Weird thing is with the fronts up in the air and rotating the ABS/ASR should be going mental. 

1 minute ago, Tech1e said:

Weird thing is with the fronts up in the air and rotating the ABS/ASR should be going mental. 

 

Yes, you are right. It should be. Haven´t thought about that before now. But It doesn´t.

 

We have tested the car with two different scan tools. My cheap one and my friends more expensive one. And they both detect the same error - 16885. 

 

Cars are sometimes a mystery to me. 

Finally I got the problem resolved.

 

I talked to a guy that renovates ABS modules, and he told me that the error 16885 could be caused by a faulty ABS module. So that it would not be the wheel bearing, sensor or the wiring that was bad. But the module itself.

So I bougt a refurbished ABS module from Ebay Germany, and replaced the old one. The error was fixed and the ABS light went off.

 

Thank you for all the input and discussions.

 

Regards, Søren